The front of the damaged digging machine for the Highway 99 tunnel project sits at the bottom of an access pit in March 2015 in Seattle. Crews were dismantling the front of the machine so they could bring it to the surface in three pieces and repair broken parts. Elaine ThompsonAP

The front of the damaged digging machine for the Highway 99 tunnel project sits at the bottom of an access pit in March 2015 in Seattle. Crews were dismantling the front of the machine so they could bring it to the surface in three pieces and repair broken parts. Elaine ThompsonAP

A look back at Seattle’s tunnel machine Bertha

The world’s largest tunnel-boring machine is on schedule to break into daylight this spring after a tumultuous dig under downtown Seattle that is years behind schedule.

The massive drill is part of the state Department of Transportation’s multibillion-dollar plan to replace the aging Alaskan Way Viaduct, which runs about 2 miles along the city’s waterfront and could buckle in an earthquake.

Mid-2013: The launch

Never miss a local story.

Sign up today for unlimited digital access to our website, apps, the digital newspaper and more.

Bertha — nicknamed after former Seattle Mayor Bertha Knight Landes who held the office from 1926 to1928 — left Osaka harbor, Japan, on March 18, 2013, beginning a three-week trip across the Pacific Ocean.

Only a few ships in the world are capable of carrying such a heavy load.

Workers at the rear of the giant drill began installing decks of the stacked Highway 99 tunnel.

At the time, the tunnel was estimated to open to traffic at the end of 2015.

Late 2013: Bertha hits steel pipe, stalls

The machine was cruising along at the start of December 2013, roughly four months after beginning its underground voyage.

Then, the cutter head hit a long steel pipe near South Main Street on Dec. 3, which state officials later disclosed was left buried more than a decade ago by one of the Highway 99 project’s own research crews.

Three days later, Bertha overheated and failed to remove dirt, leading to a massive repair effort.

The Highway 99 tunnel contractors, Seattle Tunnel Partners, contend the pipe impact damaged Bertha. Hitachi Zosen, which manufactured Bertha in Japan, says the giant drill would have otherwise made it all the way to South Lake Union as built.

However, the state says the relatively small 8-inch-diameter pipe couldn’t have possibly caused such severe damage to a 57-foot-diameter machine.

He ordered the Highway 99 tunnel contractors, Seattle Tunnel Partners, to suspend Bertha’s drilling in January 2016, stressing the “contractual obligation to Washingtonians to drill the tunnel in the right way.”

Meanwhile, Sound Transit scrapped the names “Brenda” and “Pamela” for its boring machines across the city, digging a future light-rail route from Northgate to the University of Washington’s Husky Stadium, to distance those drills from the troubled Bertha.

The downtown drill, though, began its passage underneath the viaduct, showing steady progress.

Still, the Highway 99 tunnel’s opening was pushed back yet again — this time to early 2019.

That would mark a full decade since former Gov. Chris Gregoire chose the deep-bore tunnel option and lawmakers approved legislation to make it happen, sponsored by then-Sen. Ed Murray, now Seattle mayor.

To mark the dig’s end, the agency said crews will set up cameras at the pit to record both time-lapse images and a video stream. The public won’t be allowed in the construction zone as a safety precaution.

“We recognize that there is great interest surrounding this stage of the project, and we are working on ways to share this historic moment with the public,” the department announced in a blog post.